JP2002046424A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire having an increased braking and driving performance on icy road. SOLUTION: A recessed part 22 is formed at the center portion of a block 18 formed on a tread. By this, a contact pressure of the block 18 at the center portion when contacted with the icy road can be lowered to equalize the contact pressure through the entire surface of a tread face 20, and the braking and driving performance on the icy road can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire with improved braking / driving performance on ice.

[0002]

2. Description of the Related Art Conventionally, a pneumatic tire usually has a constant block height.

[0003] The block 100 thus formed is deformed during running on a dry asphalt road surface having a relatively large friction coefficient as shown in FIG.
2 becomes uneven (increases at the end; see FIG. 5 (A)).
It becomes difficult to transmit the braking force / driving force to the vehicle.

Conversely, on an icy road having a low coefficient of friction, the road surface is deformed as shown in FIG. 6 (B), causing uneven contact pressure as shown in FIG. 6 (A). It is difficult to transmit the braking / driving force to the vehicle. Block 1 on icy road
The deformation state of 00 is different from the deformation state of the asphalt road surface because the tread surface 102 of the block 100 slides on the ice surface having an extremely low friction coefficient in the direction of arrow A to expand. In addition, the ground pressure distribution is different from that of the asphalt road surface.

[0005]

In both the asphalt road and the icy road, the entire tread needs to be optimally grounded to the road surface.

Conventionally, tread patterns and block shapes have been improved in order to improve the performance on ice, but none of them have been satisfactory.

Therefore, an object of the present invention is to define a shape for optimizing the block height in each block existing in the tread pattern in accordance with the difference in the friction coefficient of the road surface, especially for grounding on ice. An object of the present invention is to provide a pneumatic tire that eliminates uneven pressure and improves braking / driving performance on ice. More specifically, the entire block tread surface is uniformly grounded so that a larger shearing force can be generated in the block.

[0008]

In order to solve the above-mentioned problems, the present invention according to claim 1 is directed to a pneumatic tire having a tread provided with a large number of blocks defined by a plurality of grooves intersecting each other. The cross-sectional shape of the block is
At least in one section, the center of the block is concave with respect to the tire contour shape.

Next, the operation of the pneumatic tire according to the first aspect will be described.

When the constant height block formed on the tread contacts a road surface having a low friction coefficient such as an icy road surface, the contact pressure distribution from the end to the center as shown in FIG. It is getting bigger.

From this fact, if the central portion of the block is made concave, the contact pressure at the central portion of the block can be reduced, and the contact pressure on the tread surface of the block on ice can be made uniform. As a result, braking / driving performance on ice is improved, and steering stability can be improved.

FIG. 5 shows the distribution of the contact pressure when the fixed height block formed on the tread contacts a relatively high friction coefficient road surface such as a dry asphalt road surface.
As shown in (A), it is very large at the end and slightly large at the center. Therefore, if the block central portion is formed in a concave shape, the ground pressure at least in the vicinity of the block central portion can be equalized even when the block is grounded on a road surface having a relatively large friction coefficient.

According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, a depth of a deepest portion of the concave portion measured from the tire contour shape is 1.5 mm or less. I have.

Next, the operation of the pneumatic tire according to claim 2 will be described.

By setting the depth of the deepest portion of the concave portion to 1.5 mm or less, high performance on ice can be maintained.

If the depth of the deepest portion exceeds 1.5 mm, the contact pressure at the center of the block may be too low, and if it is too deep, the performance on ice may deteriorate.

According to a third aspect of the present invention, in the pneumatic tire according to the first or second aspect, the depth of the concave portion smoothly decreases gradually from the central portion of the block toward the edge of the peripheral portion of the block. It is characterized by doing.

Next, the operation of the pneumatic tire according to the third aspect will be described.

When the fixed height block formed on the tread contacts a road surface having a low friction coefficient such as an icy road surface, the contact pressure distribution from the end to the center as shown in FIG. It is getting bigger. Therefore, by gradually decreasing the depth of the concave portion from the center of the block toward the edge of the peripheral portion of the block, it is effective for equalizing the contact pressure.

According to a fourth aspect of the present invention, in the pneumatic tire according to any one of the first to third aspects,
The block is characterized in that its periphery is substantially parallel to the tire contour shape.

Next, the operation of the pneumatic tire according to claim 4 will be described.

When the grounded block undergoes a shearing deformation due to a braking force or a driving force, if the entire tread surface of the block is formed into a simple concave shape, the rigidity of the block edge is insufficient, and local deformation occurs, and conversely, the ground contacting is made. Pressure may rise.

Therefore, in such a case, the vicinity of the periphery of the block is substantially parallel to the tire contour shape,
It is preferable not to reduce the rigidity of the block edge. The term “substantially parallel” used herein includes an inclination of 3 degrees or less.

According to a fifth aspect of the present invention, in the pneumatic tire according to any one of the first to fourth aspects,
The peripheral portion is a region within 30% of the tread length in the block cross section from the block end.

Next, the operation of the pneumatic tire according to claim 5 will be described.

When the peripheral portion is longer than 30% of the tread surface length in the block cross section from the block end, the proportion of the concave portion occupying the block tread surface is reduced, and it is impossible to equalize the contact pressure.

According to a sixth aspect of the present invention, in the pneumatic tire according to any one of the first to fifth aspects,
The block has a chamfered portion at a peripheral end.

Next, the operation of the pneumatic tire according to claim 6 will be described.

By providing a chamfer at the edge of the peripheral portion of the block, the performance on ice can be further improved.

According to a seventh aspect of the present invention, in the pneumatic tire according to any one of the first to sixth aspects,
The chamfered depth of the chamfered portion is not more than the depth of the deepest portion of the concave portion.

Next, the operation of the pneumatic tire according to claim 7 will be described.

When a chamfer is provided, the chamfer depth is set to be equal to or less than the depth of the deepest portion of the concave portion,
High on-ice performance can be maintained.

If the chamfering depth of the chamfered portion is deeper than the depth of the deepest portion of the concave portion, it is difficult to obtain high performance on ice, and if it is too deep, the performance on ice may deteriorate.

According to an eighth aspect of the present invention, in the pneumatic tire according to the sixth or seventh aspect, the chamfered depth of the chamfered portion is 0.75 mm or less.

Next, the operation of the pneumatic tire according to claim 8 will be described.

By setting the chamfering depth of the chamfered portion to 0.75 mm or less, high performance on ice can be maintained.

The chamfered portion has a chamfering depth of 0.75 m.
If it exceeds m, high on-ice performance may be difficult to obtain, and if it is too deep, conversely on-ice performance may deteriorate.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] The first embodiment of the present invention
The pneumatic tire according to the embodiment will be described in detail.

Hereinafter, this embodiment will be described with reference to FIGS.

As shown in FIG. 2, the pneumatic tire 10
Has a cylindrical tread 12 straddling a pair of left and right sidewalls (not shown).

The tread 12 has a tire circumferential direction (arrow P).
Direction) and a plurality of lug grooves 1 formed along the tire width direction (arrow W direction).
6 are formed.

A plurality of blocks 18 are defined by the main groove 14 and the lug groove 16.

The blocks 18 are formed in a square rectangular parallelepiped shape in which the length of the tread surface 20 in the tire width direction is equal to the length in the tire circumferential direction.

In this embodiment, the block 18
The tire width direction dimension is 30mm and the tire circumferential dimension is 30
mm and the height is 10 mm.

A depression 22 is formed in the tread surface 20 of these blocks 18 as shown in FIG.

The concave portion 22 of the present embodiment is the lowest at the center of the block, and the depth gradually decreases gradually toward the peripheral edge of the block.

Here, the depth d1 of the deepest portion of the concave portion 22 measured from the tire outer contour 24 indicated by the imaginary line is 1.5 mm
The following is preferable, and the depth d1 of the deepest portion of the concave portion 22 in this embodiment is set to 0.5 mm. (Function) By forming the pneumatic tire 10 in this manner, the following functions are provided.

That is, when the ground 18 is grounded on a road surface having a relatively low coefficient of friction, such as an icy road surface, the concave portion 22 is formed in the central portion of the tread portion 20 where the ground contact pressure increases. The contact pressure on the tread surface 20 can be made uniform.

Therefore, braking / driving performance on an icy road surface can be improved, and steering stability can be improved. (Test Example 1) Here, a test was conducted to confirm the effects of the present embodiment.

The test tire has a size of 205 / 55R16.
Of the tire of Example 1 (the pneumatic tire described in the first embodiment) and Conventional Example 1 in which a block is not provided with a concave portion.
Tires.

In the test, the tire was mounted on an actual vehicle, and the braking distance was measured on an icy road test course.

The evaluation was performed by setting the braking distance of the tire of Conventional Example 1 to 1
The exponent was set to 00.

The smaller the numerical value, the shorter the braking distance on an icy road, and the more excellent the braking performance on an icy road.

When the difference between the indices is 10 or more, the difference is a clear difference, so that a clear superior difference due to the concave shape can be confirmed.

[0055]

[Table 1] (Test Example 2) A plurality of tires having different depths d1 at the deepest portion of the concave portion 22 were prepared, and the braking distance was measured in the same manner as in the above-described test example, and the optimum depth d1 at the deepest portion was confirmed.

[0056]

[Table 2] From the test results, it can be understood that the superiority can be clearly determined when d1 is set to 1.5 mm or less. The reason for this is considered to be the uniform effect of the ground contact pressure due to the concave shape and the effect of expanding the ground contact area when the block bends under load, but if the concave portion is too deep, it does not touch the road surface near the center of the block. It is considered that a large shearing force (maximum when not slipping on the road surface) cannot be generated on the block 18 because of the lifting. [Second Embodiment] A second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the second embodiment, as shown in FIG.
In the tread surface 20 of the block 18, the concave portion 22 is formed only near the center of the block, and the peripheral portion of the block is a flat portion 20A that matches (is parallel to) the outer contour of the tire (that is, a portion where the concave portion 22 is not provided). .

The peripheral portion of the block is an area within 30% of the tread length L in the block section from the block end. (Test Example 3) Embodiment 9 in which a flat portion is provided around the block
(The tire of the second embodiment) was prepared, and a test similar to that of the first embodiment was performed. The test results were as shown in Table 3 below.

[0059]

[Table 3] Example 9 in which a flat portion is provided around the block based on the test results
Tires have improved performance. The reason for this is that in a simple concave shape (Example 1) that receives a shear input, the rigidity of the block edge is insufficient, local deformation occurs, and the contact pressure may increase. [Third Embodiment] A third embodiment of the present invention will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 4, in the third embodiment,
The block 18 is provided with a concave portion 22 and a chamfered portion 24 is provided on the entire peripheral edge (in the peripheral portion of the block). (Test Example 4) In order to confirm the effect of the chamfered portion 24, a plurality of tires having different chamfering depths d2 were prepared, and the same test as in the first embodiment was performed. The test results are shown in Table 4 below.
As shown in FIG.

[0061]

[Table 4] From the test results, it is understood that the chamfering depth d2 of the chamfered portion 24 is preferably set to be smaller than the depth d1 of the deepest portion of the concave portion 22, and particularly preferably 0.75 mm or less. (Test Example 5) Also, a flat portion 20A in the block cross section was used.
A plurality of tires having different lengths r1 were prepared, and the same test as in the first embodiment was performed. The test results were as shown in Table 5 below (provided that d1 = 1 mm and d2 = 0.1).
mm).

[0062]

[Table 5] From the test results, it can be seen that a great effect can be obtained by setting the length r1 of the flat portion 20A in the block cross section within 30% of the tread length L in the block cross section.

Note that the pneumatic tire 10 of the above embodiment is
In the above, the block 18 is rectangular, but may be another shape.

A sipe can be formed in the block 18 to further improve the performance on ice, and the pneumatic tire 10 can be used as a studless tire having high performance on ice.

[0065]

As described above, in the pneumatic tire according to the present invention, the contact pressure on the block tread surface is made uniform on a road surface having a relatively low friction coefficient, such as an icy road, and the braking / driving performance on the icy road is greatly improved. It has an excellent effect that it can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a block of a pneumatic tire according to a first embodiment of the present invention.

FIG. 2 is a tread plan view of the pneumatic tire according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a block of a pneumatic tire according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a block of a pneumatic tire according to a third embodiment of the present invention.

5A is a diagram showing a contact pressure distribution on a dry road surface in a conventional pneumatic tire, and FIG. 5B is a block deformation diagram on a dry road surface.

6A is a diagram showing a contact pressure distribution on an icy road surface in a conventional pneumatic tire, and FIG. 6B is a block deformation diagram on an icy road surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Pneumatic tire 12 Tread 14 Main groove 16 Lug groove 18 Block 20A Flat part 22 Depression 24 Chamfer part

Claims (8)

[Claims] 1. A pneumatic tire provided with a plurality of blocks on a tread defined by a plurality of grooves intersecting with each other, wherein a cross-sectional shape of the block is such that a central portion of the block at least in one direction cross-section corresponds to a tire contour shape. A pneumatic tire having a concave shape. 2. The pneumatic tire according to claim 1, wherein the deepest part of the concave portion measured from the tire contour shape has a depth of 1.5 mm or less. 3. The pneumatic tire according to claim 1, wherein the depth of the concave portion smoothly decreases gradually from a central portion of the block toward an edge of the peripheral portion of the block. 4. The pneumatic tire according to claim 1, wherein a periphery of the block is substantially parallel to a contour of the tire. 5. The pneumatic tire according to claim 4, wherein the peripheral portion is a region within 30% of a tread length in a block cross section from a block end. 6. The pneumatic tire according to claim 1, wherein the block has a chamfer at a peripheral end. 7. The pneumatic tire according to claim 6, wherein the chamfered depth of the chamfered portion is equal to or less than the depth of the deepest portion of the concave portion. 8. A chamfering depth of the chamfered portion is 0.75.
The pneumatic tire according to claim 6 or 7, wherein the diameter is not more than mm.